STATE PLANT BOARD
November 1953 E-870
United States Department of Agriculture
Agricultural Research Service
Eureau of Entomology and Plant Quarantine
CONTROL OF HEAVY INFESTATIONS
OF PURPLE SCALES ON GRAPEFRUIT TREES
By Herbert Spencer and Paul A. Norman
Division of Fruit Insect Investigations
In the Southeastern States heavy infestations of purple scales
( Lepidosaphes beckii (Newm.)) develop on grapefruit trees and on
some orange varieties, such as the Temple. This is particularly
true in the coastal districts, where trees are usually sprayed once
or twice each spring with copper fungicides and once with zinc and
manganese compounds for minor element deficiencies. These com-
pounds are added to regularly scheduled wettable-sulfur sprays, and
the combination leaves heavy residues on the leaves and fruits. These
residues favor increases of scale insects (Osburn and Spencer 1,
Spencer 2), and the heavy infestations that develop are difficult and
costly to control.
For many years oil-emulsion sprays have been used for controlling
these heavy infestations. They are effective when applied with thorough
coverage before the infestation reaches damaging levels, but inasmuch
as oil emulsion is incompatible with sulfur, it must be put on as an
extra application, and this procedure increases costs. Also, when
purple scale infestations develop in the fall and winter, oil sprays
are objectionable because of harmful effects on fruit quality and color
and the possibility of defoliation in cold or dry weather. Growers
whose trees have heavy infestations in the fall often prefer to take
the damage from the scales rather than to risk the damage from the
oil spray and increase costs by using it.
Preliminary experiments conducted during 1949 and 1950 (Spencer
_et aL 3) indicated that parathion had great promise. Two sprayings
with 1 pound of 15-percent wettable parathion per 100 gallons of water,
in March and July, allowed only a slight increase in infestation through
the year. It was evident, though, that further work was needed to
determine the number of sprayings necessary each year, and the con-
centrations, to reduce the infestations to satisfactory levels and to hold
them there. For this work a, grove of Ruby grapefruit trees near Fort
Pierce, Fla., was selected.-^
\j Norman G. Platts was the grower cooperator.
th one or
in spray on- -
nbers of living purple scales
per leaf on- -
M J 8
d for signif:
• l % Level
. r >7
Experiments in 1951
In 1951 the same trees were used, and the six programs were
1-2-0, 2-0-0, 1-1-0, 1-0-2, 0-2-0, and 1-1-1. The postbloom spray
was applied on April 2, the summer spray on June 1, and the fall spray
on November 7.
As shown in table 2, single applications of sprays containing 2 pounds
of 15-percent wettable parathion per 100 gallons, whether made in
April or in June, permitted increases in infestation. The 1-2-0 pro-
gram gave good early and midseason control, but allowed some fall
buildup. The same was true of the 1-1-0 program, except that the
buildup was greater in the fall. The 1-0-2 program gave good fall
cleanup, but allowed too much buildup in the summer. The best pro-
gram in 1951 was three applications of the 1 -pound dosage, which
reduced an infestation of 25 scales per leaf to around 4, and held it
there throughout the year. However, 4 scales per leaf is too high.
Table 2. --Control of purple scales on grapefruit trees with one, two,
or three sprays of parathion applied in 1951
Pounds of 15-percent wettable
parathion per 100 gallons
in spray on--
Numbers of living purple scales per leaf on--
Difference required for
At 5% level
At 1% level
\j Before spraying.
, 1-1-2, 1-2
he Internet Archive
- 5 -
All the parathion spray programs described above were safe for
trees and fruit, and the best of the programs prevented damage from
These experiments suggest that, on grapefruit and orange trees
sprayed with copper and nutritional materials, 2 pounds of 15-percent
wettable parathion be added to the postbloom combination spray and
1 pound each to the summer and fall wettable-sulfur sprays. After
the first year 1 pound in each of the postbloom, summer, and fall
sprays will probably be sufficient for year-round control of these
(1) Osburn, Max R., and Spencer, Herbert
1939. Effect of spray residues on scale-insect populations.
Jour. EcoruEnt. 31: 731-732.
(2) Spencer, Herbert
1939. Increases in citrus scale-insect infestations from heavy-
residue and from copper spray mixtures. Jour. Econ.
Ent. 32: 686-688.
(3) Osburn, Max R., and Norman, Paul A.
1952. Control of purple scale on citrus with parathion. U. S.
Dept. Agr. Cir. 896, 10 pp.
: -2 62